Lighting devices that use light emitting diodes (LEDs) are becoming increasingly common in many lighting applications. Generally, LEDs use phosphor conversion of the primary emission to generate white light, but phosphors can also be used to create more saturated colors like red, green and yellow.
A conventional problem found in phosphor converted LEDs is the uncontrolled angular dependency and color non-uniformity of the light that is produced. Typically light that is emitted from the side of a phosphor layer or light at higher angles from the phosphor layers will have longer wavelengths, i.e., more light is converted, that the light that is emitted from the top of the phosphor layer, as light that is top emitted light is more direct and has less opportunity to be converted by the phosphor. The result is that the color of the emitted light is angularly dependent.
Current strategies for dealing with the color non-uniformity include reducing the angular dependency. By way of example, one strategy is to coat the sides of the phosphor material to prevent the side emission of light. Another strategy is to add scattering particles to the phosphor material to mix the converted and non-converted light so that the side emitted light and top emitted light have approximately the same color. Such solutions to the angular dependency, however, reduce the efficiency of the devices as well as increase the cost of production. Accordingly, other solutions for dealing with the angular dependency are desired.